1. Field of the Invention
The present invention relates to a laser-sensitive polymer for data storage, a data storage media coated by the same, and a data storage device and method using the data storage media. In particular, the present invention relates to a polymer for data storage comprising two of the functional group of disperse red 1, which is a photoresponsive organic dye, bonded to a branched chain per every repeat unit, a data storage media coated by the same, a reversible and optical data storage device containing a thin film, and a data storage method using the device.
2. Description of the Related Art
In general, an optical data storage method involves a data storage media consisting of short wave-length laser and organic dyes sensitive to the same, of which method has a benefit of high density data storage. Taking advantage of properties of the organic dyes, e.g. easy structural transformation and an excellent processability for manufacturing thin films, the inventors discovered a reversible and optical data storage method using a data storage media for which the organic dyes or optical polymers containing the dye compounds as a substituent is applied. (Refer to U.S. Pat. Nos. 5,262,081, 5,445,853, 5,296,321, 4,666,819 and 5,384,221, German Patent No. 3623395, British Patent No. GB 2. 146787A, and Japanese Laid-Open Publication 1-294791.)
The basic principle of a reversible data storage method capable of data record-erase-read-rewrite is that when laser is irradiated to a data storage media containing organic dyes, the dyes go through color changes, birefringence changes and phase transition (e.g. crystal form  amorphous form or isotropic form  anisotropic form), depending on molecular structures thereof.
Well-known organic dyes for the technology described above include cyanine, phthalocyanine, squarilium, dithiol metal complex salt, quinone, spiropyran and azobenzene, and so forth.
The similarity in the molecular structure of each compound listed above is that each compound contains a different polar group that causes dipole moment. Thus, when a data storage media coated with one of the compounds above is irradiated by a polarized light with a particular wave-length, the molecules are arranged perpendicular to the plane of polarization of the irradiated light, which is basically due to the attractive force between dipole moments in a polar group. In this way, the newly arranged molecules go through the three optical changes aforementioned, and using this principle, data can be recorded in a data storage media.
The organic dyes applied to a data storage media, depending on a polar group""s molecular structure, absorb ultraviolet or infrared having a wavelength 300 nm to 800 nm. Therefore, in order to develop an appropriate data storage element, it is important to choose a light source with particular wavelengths that causes optical changes in the data storage media.
Typically used light source for an optical data storage is a laser like Ga/As, Hexe2x80x94Ne, Ar ion, Nd/YAG or Hexe2x80x94Cd, having a wave-length of 780 nm, 630 nm, 488 nm, 514 nm, 360 nm or 325 nm.
However as for Compact disc (CD) or Laser disc (LD), for which an optical data storage media is applied, only 780 nm Ga/As and 630 nm Hexe2x80x94Ne have been commercially used as a minor light source for a disc drive. Unfortunately, when these lights with longer than 600 nm wavelength are used as a recording light source for an optical data storage device, since the lights oscillate relatively long infrared, data storage density gets decreased thereby.
This problem occurs typically during the process of recording data, if an organic dye compound containing thin film is irradiated by polarized recording light having long wave length, the irradiation area of a data storage media is enlarged as compared with a short wave length light source. Therefore by using Ar ion laser of which wave length is below 520 nm as a recording light source, the area of a data storage media becomes small and data storage density per unit area is increased.
Attempts to increase data storage density as described above have been made by developing a polymer in which a functional group of azobenzene base organic dye compound is bonded to a branched chain, which is sensitive to a short wave length in a range from 300 nm to 400 nm. Thus, the inventors researched on the applications of a reversible and optical data storage media to the above polymer compound and were granted a patent in Korea (Korean Patent No. 77801, Application filing date: Feb. 27, 1991), and in relation to this, another application (Korean Patent Application No. 40216, Filing date: Aug. 22, 1997) was already laid open.
The basic mechanism behind the above technology is that a polymer having azobenzene base compound bonded to a branched chain coated a substrate to manufacture a thin film, and low output polarized ultraviolet was irradiated to the thin film. In result, it was possible to record data in high density with excellent resolution and new data could be rewritten after easing the previous data.
The media described above showed much improved resolution and recording speed by hundreds of nanosecond) as compared to those of prior art (U.S. Pat. No. 5,173,381) and German Patent No. 3,623,395: U.S. Pat. No. 4,837,745 and Japanese Publication No. 63-87626).
The pulse laser was observed as very beneficial not only that it was based on the molecular structure of a polymer compound employed, but also that it made it possible to record high density data at a speed of hundreds of nanosecond faster than others by using Nd/YAG pulse laser as a recording light, which usually oscillate a ultraviolet with 365 nm within 10 nanosecond.
Despite the benefits described above, because the short wave length pulse laser uses inorganic single crystal, thus making it expensive and big, it is considered rather inappropriate oscillation material for a compact sized data storage device.
Therefore, attempts to solve the cost and size problems, by applying Ar ion laser of which wave length can be modulated and is not expensive, have been made active for applying to a compact data storage device.
It is, therefore, an object of the present invention to provide a polymer compound for data storage.
Another object of the present invention is to provide a data storage media using a substrate coated with such polymer.
Still another object of the present invention is to provide a data storage device for data write/read into such data storage media and a data storage method thereof.
To achieve the above object, there is provided 5 polymers for data storage: a polymer in which two of the disperse red 1 functional group, which is illustrated in Chemical formula 1, are bonded to a branched chain per each repeat unit, and four other polymers which are illustrated in Chemical Formulas, 2 to 5, respectively. 
wherein n is a integer; m is 2, 4, 6, 8 or 10; R is the disperse red 1 functional group; 
and the average molecular weight of the polymer is in the range of from about 2,000 to 15,000. 
wherein n is an integer; two xe2x80x94CH2xe2x80x94 are bonded to a benzene ring in orto-, meta- or para-position in the above
R is the disperse red 1 functional group 
and the average molecular weight of the polymer is in the range of from about 2,000 to 15,000. 
wherein n is an integer; R is 
and the average molecular weight of the polymer is in the range of from about 2,000 to 15,000. 
wherein R is 
the ratio of X:Y is 3xcx9c97 mol %: 97xcx9c3 mol % and the average molecular weight of the polymer is in the rage of from about 2,000 to 15,000.
Preferably, the average molecular weight of the polymers which are illustrated in Chemical Formulas 2 to 5 is in the range of from about 3,000 to 10,000, respectively.
In addition, preferred ratio of X:Y in the polymer of Chemical Formula 5 is 5xcx9c30 mol %: 95xcx9c70 mol %.
The present invention provides a blend copolymer for data storage, which is prepared by mixing one of the polymers illustrated in Chemical Formulas 2 to 5 to either polymethylmetacrylate or polyvinylcarbazole in the tetrahydrofaran(THF) aqueous solution.
Here, the polymer selected from Chemical Formulas 2 to 5 can be added 5% to 30% by weight of the above blend copolymer.
Another aspect of the present invention provides a reversible optical data storage device, which comprises an Ar ion laser light source 2; a polarizing plate 15 on which blue laser irradiated from the light source 2 gets incident; an optical attenuator 13 on which the blue laser that passed through the polarizing plate gets incident; a wave plate 12 on which the polarized light that passed through the optical attenuator gets incident; and a data storage media 6, which is coated with the polymer for data storage in accordance with the present invention, and located in the path of the polarized light that passed through the wave plate.
Here, the above described data storage media is formed by comprising the steps of:
(a) dissolving the polymer aforementioned into an organic solvent and coating a substrate;
(b) heating the substrate at the polymer""s specific melting point; and
(c) cooling the substrate below the glass transition temperature (Tg) to fixate the polymer""s isotropic state.
In the above device, the Ar ion laser light source emits 400 nm to 520 nm short waves.
For the data storage device described above, sound optical modulator can be additionally placed between the optical attenuator 13 and the wave plate 12 in order to screen the Ar ion polarized light transmission, so that data recording speed can be reached down to 1 microsecond.
Still another aspect of the present invention provides a reversible optical data storage device, which comprises an IR laser light source 2; optical lenses 3 and 4, on which the irradiated light gets incident; a first polarizing plate 5, on which the light from the lens gets incident, a data storage device 6, which is coated with the polymer for data storage in accordance with the present invention, and located in the path of the light that passed through the first polarizing plate 5; a second polarizing plate 7, which is located in the path of the light that passed through the media 6, and has a polaroid axis perpendicular to that of the first polarizing plate 5; and an output device, which outputs the data stored on the media 6 by inputting the light emitted from the second polarizing plate 7.
In a broad sense, xe2x80x9ca data storage devicexe2x80x9d throughout the specification indicates a device with the capacity of data record and/or data read, and preferably, the data storage media described above is prepared by the method explained here.
The preferred IR laser light source is either 847 nm Ga/As or 633 nm Hexe2x80x94Ne. The data storage media is positioned at an angle of (1+n)xcfx80/4(n is 0, 2, 4 or 6) with the polarization axis of the first polarizing plate and that of the second polarizing plate, respectively.
The output device further comprises a digital voltmeter 10, and a computer 16 for processing the detected current intensity according to time, thus data record and data read data can be performed concurrently.
Another embodiment of the present invention provides a reversible optical digital data storage method, which comprises the steps of:
(a) coating a substrate with the polymer according to the present invention;
(b) heating the coated substrate at a temperature higher than the employed polymer""s melting point in order to arrange the substrate in the isotropic state, and form a data storage media by cooling the same below the glass transition temperature (Tg) of the polymer employed;
(c) recording digital data in the data storage media by passing through the polarized light that was irradiated from Ar ion laser light source a first polarizing plate, an optical attenuator and a wave plate successively;
(d) reading the digital data by inputting the digital data to an output device after passing the polarized light irradiated from an IR laser light source through an optical lens, a second polarizing plate, the data storage media, and finally a third polarizing plate which has a polarization axis perpendicular to that of the second polarizing plate;
(e) erasing the recorded and read digital data from the data storage media;
(f) rewriting and re-reading new data by repeating the steps of (c), (d) and (e) in the data storage media.
Yet another embodiment of the present invention provides a reversible optical analogue data storage method, which comprises the steps of:
(a) coating a substrate with the polymer according to the present invention;
(b) heating the coated substrate at a higher temperature than the polymer""s melting point in order to arrange the substrate in the isotropic state, and form a data storage media by cooling the same below the glass transition temperature (Tg) of the polymer employed;
(c) recording analogue data in the data storage media by passing through the polarized light that was irradiated from Ar ion laser light source a first polarizing plate, an optical attenuator and a wave plate successively;
(d) reading the analogue data by inputting the analogue data to an output device after passing the polarized light irradiated from an IR laser light source through an optical lens, a second polarizing plate, the data storage media, and finally a third polarizing plate which has a polarization axis perpendicular to that of the second polarizing plate;
(e) erasing the recorded and read analogue data from the data storage media;
(f) rewriting and re-reading new data by repeating the steps of (c), (d), and (e) in the data storage media.
The digital or analogue data storage media is positioned at an angle of (1+n)xcfx80/4(n is 0, 2, 4 or 6) with the polarization axis of the second polarizing plate and that of the third polarizing plate, respectively.
During the process of reading the analogue data on the thin film, it is preferred to use a low output polarizing microscope where the second polarizing plate and the third polarizing plate are perpendicularly attached.
Preferably, the erasing the digital or analogue data process of step (f) is carried out by erasing the data in the data storage media by passing the circular polarized light through the media, which was emitted from the wave plate having xcex/4 wave length when the wave plate in the step (c) has xcex/2 wave length. Also, the digital data can be erased in the data storage media by heating the media at a higher temperature than the melting point of the polymer employed.
In the meantime, the polymer for data storage, which is illustrated in Chemical Formula 2 can be prepared by polymerizing malonic acid ester monomer illustrated in Chemical Formula 6 and CmH2mBr2 (m is 2, 4, 6, 8 or 10) in which brome is substituted with the first carbon and the mth carbon. 
wherein R is 
The polymer for data storage, which is illustrated in Chemical Formula 3can be prepared by polymerizing malonic acid ester monomer illustrated in Chemical Formula 6 and xylen having two substituted brome. 
wherein R is 
The polymer for data storage, which is illustrated in Chemical Formula 4 can be prepared by polymerizing silicate ester monomers illustrated in Chemical Formula 7. 
wherein R is 
The polymer for data storage, which is illustrated in Chemical Formula 5 can be prepared by polymerizing silicate ester monomer and methylmetacrylate (MMA).
The preferred glass transition temperature (Tg) of polymers is in a range of from about 20 to 100xc2x0 C.
The maximum absorption wavelengths of the monomers and polymers employed in the present invention are in a range of from about 450 nm to 500 nm. Thus, the polymer in the invention can absorb the blue light, which was oscillated from Ar ion laser and cause an optical change, e.g., birefringence, at a maximum speed.
The present inventors have found that when the polymer of the Chemical Formula, having two of xe2x80x94CH2xe2x80x94 in para position in the benzene rig in particular, and the polymer of the Chemical Formula 5 are respectively employed in a data storage media, the data storage media demonstrated excellent data storage stability even at 80xc2x0 C. outside.
The R group, that is, organic dyes, in the polymers of the present invention is 60% to 80% by weight of repeat units in the polymer, which is relatively higher than 15% to 40%, typically observed values in prior arts (U.S. Pat. Nos. 4,551,819, 5,024,784, and 5,173,381; German Patent No. 3623395; Japanese Patent Publication No. 63-87626). In other words, the polymers in the present invention contain more functional groups with optical properties in high density.
To be short, the polymers according to the present invention are prepared to be able to record the data in microsecond and enhances the data stability. Also, the data storage device employing the polymers aforementioned demonstrates much improved data recording speed and data storage stability as compared to that of prior arts.